1. Field of the Invention
The field of the invention relates to patient breathing systems generally, and more particularly, to a patient breathing system that includes a ventilator that provides driving gas flow to generate patient inspiration.
2. Description of Prior Art
As described above the invention relate to patient breathing systems. Patient breathing systems in anesthesia are classified as non-re-breathing and re-breathing breathing systems.
In non-re-breathing systems the gas mixture is supplied to the breathing system and inhaled directly by the patient. When the patient exhales all the exhaled gases are scavenged. The breathing system is very simple and reliable, but if expensive anesthetic inhaled drugs are used the non-re-breathing systems are very un-economical. The required fresh gas is the same as the minute volume for example for an adult about 6 l/min.
The re-breathing systems are divided into two subcategories either without or with carbon dioxide absorption.
In the re-breathing patient breathing systems without carbon dioxide absorption fresh gas is fed to the patient close to the airway. The exhaled gas moves in the ventilation hose toward the ventilator or manual ventilation bag. The fresh gas does not to a significant extent mix with the exhaled gas. In order for the patient gas to be separated from the driving gas of the ventilator there is usually either a descending or ascending bellows. In some ventilators the manual ventilation bag serves as a reservoir. During the expiratory pause the fresh gas flowing is further pushing the exhaled gas away from the patient and at the same time filling the ventilation hose with fresh gas for the next inspiration. Excess gas is scavenged through and pop-off valve. During the inspiration the fresh gas in the hose is first inspired and when that is used exhaled gas is inspired for a second time mixed together with the continuous flow of fresh gas. Re-breathing systems have been described by for example Mapleson and Bain in the book Pediatric anesthesia edited by George A. Gregory, 3rd ed., ISBN 0-443-08904-3. A benefit of the re-breathing system without carbon dioxide absorption is that it is relatively simple. The consumption of fresh gas is somewhat lower than with a non-re-breathing system, the fresh gas required is approximately 50-75% of the minute volume.
The re-breathing patient breathing systems with carbon dioxide absorption are the most economical breathing systems where the fresh gas flow may be reduced to as low as the uptake of the patient. At the same time these systems are the most complex breathing systems. Basically this system comprises of a circle breathing system including a fresh gas inlet, inspiratory check valve, inspiratory hose, y-piece for patient connection, expiratory hose, expiratory check valve, ventilator connection and carbon dioxide absorber for removal of the exhaled carbon dioxide. The inspired gases consist of both new fresh gas and re-breathed exhaled gases from which the carbon dioxide has been removed. As new fresh gas is introduced to the breathing circuit some of the gas is taken up by the patient. The excess of gases is directed to the scavenging through the pop-off valve in the ventilator. In order for the patient gas to be separated from the driving gas (compressed air or oxygen) of the ventilator there is usually either a descending or ascending bellows. In some ventilators the manual ventilation bag serves as a reservoir and there might be either a piston or compressor in line as a ventilator. The consumption of fresh gas can in a circle breathing system be close to the uptake of gases, this can practically during the maintenance of the anesthesia be as low as less than 10% of the minute volume.
As the circle breathing systems are the most economical to use during inhaled anesthesia they are very common. At the same time the systems used are the most technically complex ones of the breathing systems. Complexity of the prior art systems leads to high demands for example in maintenance, which in turn leads to increases in costs. Owing to said facts high costs are one of the main disadvantages of the prior art.
The design of the ventilator is also quite challenging and it is difficult to design all the same ventilation modes as the bellows and pop-off valve causes disturbances and have to be considered when implementing the ventilation modes. This also leads to high costs.
Hospital infections are a big concern in today's world with the avian flu. The invention simplifies the cleaning of the breathing system as many parts are not required when compared to the systems of the prior art. The extended distance can be made as a disposable part, easy to clean and easily equipped with a microbe filter.
FIG. 1 shows schematically an example of a typical example of the breathing system of the prior art. Reference number 1 shows a patient and reference number 2 shows a ventilator. Reference number 3 shows an inspiratory hose and reference number 4 an expiratory hose. Reference number 5 shows a y-piece through which the inspiratory hose 3 and the expiratory hose 4 are connected to the patient. Reference number 6 shows a fresh gas inlet connected to the inspiratory hose.
The inspiratory hose 3 and the expiratory hose 4 form a circle through which expired gases can be circulated back to the patient. The circle formed by inspiratory hose 3 and the expiratory hose 4 are further provided with an arrangement for enabling the gas flow in a desired direction. Said arrangement can comprise inspiratory check valve 7 and an expiratory check valve 8 as shown in FIG. 1. Said arrangement can alternatively comprise a compressor, a fan, an ejector or some other appropriate arrangements. The circle comprises also a ventilator port 9 for the ventilator connection, and a unit for removal of the exhaled carbon dioxide. Said unit can be a carbon dioxide absorber 10 as shown in FIG. 1 or alternatively for example a membrane arrangement.
The patient breathing system comprises also an arrangement 11 by which driving gas of the ventilator 2 has been separated from the patient breathing gases flowing in the circle formed by the inspiratory hose 3 and the expiratory hose 4. In the example shown in FIG. 1 said arrangement is formed by a bellows or bag placed in a bottle. The bellows has typically a volume of about 2.5 litres and height of about 30 cm. The pipe between the bellows and the circle has typically a length of 1 m and a volume of 0.5 litre.
In the system shown in FIG. 1 the driving gas is in the space between the bellows and the bottle, and the patient gases are in the bellows, i.e. the bellows completely separates the driving gas from the patient gases.
Reference number 12 shows a pop-off valve through which the excess of gases is directed to scavenging.
The matters described above and operation of the system described in FIG. 1 are well known to a person skilled in the art.
The system shown in FIG. 1 has the disadvantages of the prior art described earlier in the text.